For all music from a simpler time- much simpler- that you still find undeniably epic.
PS: I don't exactly see how dying en masse from Bubonic plague, getting bullied by local gentries, lords, and knights, and fearing that a dragon is going to snap your head off your neck or a witch is going to bubble your heart out your throat is considered "simpler", but whatever works. Dio was obsessed with it, and so is all of power metal, so there must be some humble allure.

And Blackmore's Night does qualify. Medieval doesn't mean only in medieval times.
EDIT: And don't just stop with medieval. Go back to the first goddamn rocks banged against rocks if you have to.
http://www.youtube.com/watch?v=DBhB9gRnIHE

I don't know how much music that's actually from centuries ago is going to be posted, seeing as there's not a whole lot surviving, but Falls of Rauros, particularly this song, always reminded me of a less complicated, easier time when nature ruled the land. Wyrd's Heathen evokes similar feelings for most of its duration.

I really enjoy these performances of early musical works (as well as the entire albums for these tracks):

http://www.youtube.com/watch?v=5-Cej8Kb5DE
http://www.youtube.com/watch?v=ccBpe0FpHr8
http://www.youtube.com/watch?v=robXU_chDTM

The Moon Lay Hidden Beneath a Cloud is the ultimate in medieval sounding music.

I always love when modern music has this kind of feel to it. I really enjoyed obsequiae's suspended in the brume of eos- metal chamber music in essence.

Of the wand and the moon, particularly nighttimes nightrhymes reminded me of this feel too.

It's a pretty basic thing but often it seems like vivid medieval imagery on album art helps a lot in creating this kind of atmosphere.

Pagan Alter give off a very ancient vibe... I don't think that's what you mean though. Godkiller are pretty cool for medieval thing.

Yeah, having the whole electric guitar thing, Pagan Altar are pretty wide of the mark. Unless I'm misreading things here, I think OP is talking about legit early music rather than even stuff like Dead Can Dance/Arcana etc, let alone BM or more Metal-orentated stuff.

On topic, I have a modest collection of Hildegarde von Bingen, various plainsong recordings, a few cd's of provincale trubador songs, and probably my favourite - an album called "Christmas at Saxon winchester", which is a combination of latin and anglo-saxon pieces.

I dig some von Bingen and Machaud. This is pretty old: http://www.youtube.com/watch?v=Wh6vVnWLvmU. I think it's a motet.

I just discovered some *really* ancient sounding music- recently made, but it's ancient as in 'Antiquity' ancient, and yes, it's the most badass thing I've ever heard.

Synaulia is the primary one
http://www.youtube.com/watch?v=uJLXyBzMci0‎

Roman music kicks ass.

Daemonia Nymphe is an amazing Greek folk group. Authentic instruments. Krataia Asterope is a classic album from them.

Irfan are the Bulgarian folk equivalent of Daemonia Nymphe-- definitely recommended. I'd say their second album, Seraphim, is flawless.

Beleño. Asturian traditional folk
http://www.youtube.com/watch?v=T039zMWf4Ds
http://www.youtube.com/watch?v=9LkR8KGhhkY

Sturmpercht, more experimental and modern sounding, but heavily influenced by alpine traditional songs
http://www.youtube.com/watch?v=6rgwQekl29w
http://youtu.be/HeEcS2Q2Ofw
http://www.youtube.com/watch?v=SVadY0VLHx4

Andean folk music seriously rules. I particularly like the peruvian group Wayanay Inka
http://www.youtube.com/watch?v=gI6YAaq6HG0
http://www.youtube.com/watch?v=UB0JXfaYgG4
http://www.youtube.com/watch?v=NVZjkA_O2ew

I don't know any actual medieval music other than gregorian chants, byzantine church music and trobadour songs

I have a huge interest in early music, so I can offer a few recommendations for anyone with a similar intetest.

For ancient Roman and Greek music, I thoroughly recommend having a trawl through the many albums of Michael Levy, an artist who specialises in the lyre and harp:
http://michaellevy.bandcamp.com/

In terms of Gregorian / medieval chant, I have obtained several chant albums over the years, of varying quality. The albums I enjoy the most seem to feature a smaller group of singers, which gives atmospheric clarity to the performance. Many of the budget albums you find in shops tend to feature larger groups of singers, which tends to dull the sound.

Two of the best chant albums I have found are "Kyrie - Chant for Quiet Meditation" and "Sanctus - Music for Quiet Contemplation". Both of these are on the Gift Of Music label, whose releases are usually in that rather twee "past times" vein. These two albums however, are excellent. They both feature some of the most atmospheric chant I've heard, interspersed with some beautifully evocative instrumental medieval pieces. Both albums can usually be found for ultra-cheap prices in the "new&used" section of Amazon. Go get them, they are highy recommended.

Anyone interested in some (more weird/odd) medieval sounding music, I suggestGaë Bolg And The Church Of Fand.
Very much "trumpet based" stuff and absolutely great. The three albums "John Barleycorn Must Die", "Tintagel" and
"La Ballade De L'Ankou" are all worth checking out...

I actually own Gaë Bolg's (sans "And the Church of Fand"), 'Aucassin Et Nicolette' but I found it severely underwhelming at first and really quite boring even on later listens. The whole album just felt like unnecessary Sol Invictus worship (which I suppose shouldn't be surprising, as its main man is the trumpet player of Invictus).

Never checked out any other of his outputs thanks to that terrible first impressionm, though; I guess I probably should.

Daemonia Nymphe as someone said
Another I stumbled upon was Goliard, a UK duo who play mainly French and German medieval music. Their album Fortune My Foe is excellent